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Finite difference time domain simulation tools offer unique capability for the study of RF antennas in fusion-scale experiments, because of their traditional focus on accurate detailed representation of 3D geometry.
This talk will present our efforts to apply such a code to the modeling of antennas on MST, NSTX, CMod, and ITER. RF sheaths on or near the antenna are believed to be responsible for impurity production, a major concern for fusion experiments. These same sheath effects are also key to producing non-thermal electron populations which maintain ionization in some industrial plasmas.
The talk will show how we use sub-grid models to represent the RF and rectified sheath, and how we plan to combine this with test particles to model non-thermal physics. Finally, while performing such simulations, an observation of strong slow-wave excitation in a thin layer near the antenna has also led to questions of whether such waves might be a contributor to parasitic losses from these antennas, e.g., in NSTX. The talk will discuss this hypothesis, and on-going modeling efforts aimed at better understanding it.